Polyvinyl acetal resins



,tion of resinous condensation products Patented July 7, 1953 POLYVINYL ACETAL RESINS Herman S. Bloch, Chicago, Ill., assignor to Universal Oil Products Company, Chicago, 111., a

corporation of Delaware No Drawing. Application March 8, 1951, Serial No. 214,645

8 Claims. ((1260-73) This application is a continuation-in-part of my copending application Serial No. 750,361, filed May 24, 1947, now Patent No. 2,545,683, March 20, 1951.

The present invention relates to the producbroadly characterized as polyvinyl acetal compounds. More specifically, the invention concerns a process for producing said resins which comprises reacting an ammonia condensation product of a carbonyl compound hereinafter more specifically characterized, with a polyvinyl alcohol or a partially hydrolyzed ester thereof. The primary object of the present invention, therefore, is to provide a process for the production of said resinous condensation products wherein the above general classes of reactants are utilized.

It is another object of the invention to produce resin-like condensation products useful as moldable resins per se or as components of various compositions, as for example in the formulation of paints, varnishes, lacquers, laminates, adhesives, and the like.

Still another object of the invention is to prepare resinous products having either thermoplastic or thermosetting properties depending upon the character of the reactants utilized in the preparation thereof and upon the conditions selected for effecting the condensation reaction involved in the formation of the present acetal type of compounds.

Broadly, the invention comprises reacting at condensation reaction conditions at least a partially hydrolyzed ester of a polyvinyl alcohol and an ammonia condensation product of a carbonyl compound selected from the group consisting of the saturated and unsaturated aliphatic, alicyclic, and aromatic aldehydes and ketones.

Another embodiment of the present invention concerns a process for the production of an acetal type of resinous condensation product which comprises reacting at condensation reaction conditions a plurality of reactants consisting essentially of (1) a partially hydrolyzed polyvinyl alcohol ester homopolymer and (2) an ammonia condensation product of a carbonyl compound selected from the group consisting of the aliphatic, cycloaliphatic, and aromatic aldehydes and ketones containing no other ammonia-reactive radical than the carbonyl radical.

In accordance with one of its more specific embodiments, the invention comprises reacting a plurality of reactants consisting essentially of (1) a polyvinyl alcohol compound selected from a polyvinyl alcohol and a partially acylated-polyvinyl alcohol and (2) a condensation product of ammonia with carbonyl compound containing no other ammonia-reactive group than the carbonyl radical, at atemperature of from about 10 to about 150 C. in the presence of a mineral acid as catalyst for the condensation reaction and a solvent which mutually dissolves at least one of said reactants, thereafter removing said solvent and said catalyst and recovering from the reaction mixture the resultant polyvinyl acetal condensation product as the resinous condensation product of this invention.

Another specific embodiment of the invention relates to a process which comprises reacting polyvinyl acetate and a primary imine, the reaction beingeffected in the presence of a sufilcient quantity of hydrochloric acid to form the hydrochloride of said imine at a temperature of from about 30 to about C. and for a period of time suflicient to not only hydrolyze the polyvinyl acetate but also to effect the condensation of said polyvinyl alcohol compound and said imine to form thereby an acetal type of linkage and thereafter isolating from the reaction mixture the condensation product of the resulting acetalation reaction. 7

Other embodiments relating to specific reactants and to means for conducting the reaction will be hereinafter described in greater detail.

The reaction mechanism involved in the formation of the present resinous condensation product is believed to be essentially an acetalation reaction between a polyvinyl alcohol which may be partially acylated and an ammonia-carbonyl condensation product, the reaction being illustrated, for example, in the following general equation wherein the polyvinyl alcohol reacting component is represented by a portion of the polyvinyl chain present in the polymer and the ammonia condensation product of a carbonyl compound by an imine comprising one of the specific classes of condensation products contemplated herein.

wherein B may be hydrogen and R, and R. are selected from the group consisting of alkyl, alkenyl, cycloalkyl, aryl, aralkyl, or a heterocyclic radical. The polyvinyl reactant, represented by a segment of the polyvinyl alcohol chain in the above formula, is usually a polymer of from about 5,000 to about 100,000 molecular weight. Although some of the hydroxyl groups attached to individual carbon atoms of the polyvinyl chain may be replaced by ester groups, it is apparent,.on the basis of the reaction mechanism involved in the formation of the present acetal linkage, that at least a portion of the hydroxyl groups present in polyvinyl alcohol must remain free and non-acylated, since-acetal formation is dependent upon the condensation between a free hydroxyl group-and theammoniacarbonyl linkage of the condensation-product.

The reactant herein referred to as a polyvinyl' esters of polyvinyl alcohol-at least 90% hydrolyzed. A completely esterified organicester 'ofpolyvinyl alcohol such as the-acetate, propionate, butyrate,-sebacate, benzoate,- phthalate, etc-may also be utilized-as the polyvinyl reactant in the present condensation reaction" when reaction conditions anda' hydrolyzingagent present in the reaction mixture are selected so as to effect at least'a partial hydrolysis'of thepolyvinyl ester.

The hydrolyzing agent incorporated into the mixture of reactants when the latter completely esterified polyvinyl alcohols are employed as reactants is usuallya strong aqueous mineral acid such as'hydrochloric acid,-sulfuric acid, phosphoric acid, etc., which'not only catalyzes the condensation reaction or acetalformation but also concomitantly hydrolyzes a portion of the *esterlinkages to provide free alcohol groups essential to the acetal-forming reaction. Although it -is presumed that the acid-catalyzed reaction 'proceeds in this manner, that is by hydrolysis of the ester to liberate freealcohol groups which are subsequently acetalized, it"is possible that there is a direct reaction between the polyvinyl alcohol ester and the ammonia-carbonyl compound'condensation product, whereby, under the influence of the aqueous acid, the acetal is formed, together with free organic acid and ammonium salts.

When desired, partial or complete hydrolysis of the polyvinyl alcohol ester may be effected prior to charging the reactants into'the process and for this purpose it is desirable that atleast 25% and higher, preferably, at least 90%,- up to substantially complete hydrolysis, of the ester linkage be effected,- since in generaL: the properties of the product are directly dependent upon the extent of hydrolysis obtained either before or durin the condensation reaction. .It has been noted, for example, that by increasing the percent of hydrolysis, the softening point, tensile i strength; hardness etc. of the productis increased,

whereas the solubility of the product in various organic solvents and its flexibility is generally lowered. The above properties and others, such as the impact strength are also dependent upon 'other factors involved. in the reaction; such as the. type of carbonyl-compound utilized in the preparation of the condensationproduct' thereof .withammonia, the molecular weight of the polyvinyl-alcohol or its ester and the'degree of cross- .linking or bridging obtained during the condensation r acetal-formingreaction.

. In the production of the present'resinous con- ..densation products, it has been noted that when .linkage is established,

condensation is effected under certain conditions .of operation, as hereinafter specified; the: resinous product acquires the properties of a thermosetting type of resin and it is believed that the result is dependent upon the formation of the socalled bridging or cross-linking obtained between individual polyvinyl alcohol or partial --ester molecules. The reaction mechanism for the formation of the present product, as proposed in Equation 1' above, wherein the following type of .represents but one typeof acetal linkage .ob-

tained in the condensation reaction; under conditions of reaction. in whichcross-linking. is ob- .tained, the. above type A acetal linkage is substituted atleast, partially by the. bridged. type of linkage indicated by. the. following formula:

' Formula A'above is an acetal structure formed by aicondensation' reaction occurring between the adjacent free hydroxyl groups on the same polyvinyl chain of carbon atoms and is the type of linkage usually formed. TypeA' linkage ordinarily gives rise to resins having thermoplasticproperties and relatively low melting points. Formula B represents the bridged type acetal linkage ob- "tained'by a condensation occurring between the ammonia-carbonyl reactant with free hydroxyl groups on different polyvinyl chains and is ap- "parently'formed to'a minor extent under most conditions of acetylation. Cross-linkage may be favored, however,'by the use of a relatively slight- Lly. hydrolyzed polyvinyl alcohol ester or by the-use of a polymeric ammonia-carbonyl condensation "product as hereinafter described. If the degree of hydrolysis "is small, the probability of the existence of free hydroxyl groups in the positions required to formtype A linkages is reducedyand cross linkages of the type represented by Formula B are more likely. The latter type B'linkage is believed to be involved in the formation of thermosetting resinous products "and is notnecessarily limited tocross-linkage between merely two molecules of polyvinyl reactant but may-involve a number of individual polyvinyl alcohol molecules containing a multiplicity "of hydroxyl groups resulting in the formation of large resin molecules having high melting points and-relatively low solubility in organic solvents.

By varying one or more of the factors which determine the course of reaction, that is, the reaction temperature, the degree of hydrolysis of the polyvinyl alcohol ester, the structure ofthe carbonyl compound involved in the ammonia carbonyl reaction product, the viscosity (that is, the molecular'weight) of the polyvinyl reactant and the presence or absence of a catalyst in' the "reaction mixture;'it is possible tooobtain resinous products having'a wide variation in properties ranging;from :thermoplastic 'to .ithermosetting types, from hard to soft resins, and from low melting to high melting products.

The reactant of the present resin-forming condensation reaction characterized herein as a condensation product of ammonia and a substituted carbonyl compound selected from the aldehy-des and ketones and containing no other ammonia-reactive substituents other than a carbonyl group is prepared prior to the resinforming reaction by the condensation of ammonia with an aldehyde or ketone to form a primary imine or an addition product of the re actants which is capable of regenerating the carbonyl compound in the presence of the acidic condensation catalyst utilized in the present resin-forming reaction. In the preparation of an ammonia-carbonyl reactant, suitable aldehydes and ketones may be selected broadly from the various classes of these compounds, includ ing the aliphatic, cycloaliphatic, and aromatic aldehydes and ketones such as the dialkylketones, the diarylketones and the mono-alkylmono-arylketones, in which the alkyl substituents generally contain not more than about 12 carbon atoms per alkyl group. Thus, acetaldehyde, propionaldehyde, crotonaldehyde, butyraldehyde, isobutyraldehyde and homologs are typical of the large number of aldehydes utilizable in the condensation reaction with ammonia,as well as the aromatic-substituted aldehydes such as benzaldehyde, tolualdehyde, cinnamaldehyde and others. The homologs of formaldehyde are particularly useful, especially those having up to about 9 carbon atoms per molecule, since the latter form polyvinyl acetals having useful solubility properties and have a relatively high resistance to weathering and stabiilty to light. Of the ketones utilizable in the preparation of the ammonia-carbonyl condensation product, those compounds which regenerate either the original ketone itself or a modified ketone upon treatment with a strong, relatively concentrated mineral acid may be utilized in the condensation reaction with ammonia to form the initial ammonia-carbonyl reactant of this process. Thus, the dialkylketones, such as acetone, methylethylketone, dibutylketone, etc., and the alkylcycloaliphatic ketones, such as methylcyclo-hexylketone and the dialkenyland alkylalkenyl ketones such as methylvinylketone, mesityloxide, I

phorone, etc. yield a condensation product with ammonia which either regenerates the initial ketone starting material in the presence of a strong mineral acid during the reaction of the condensation product with the polyvinyl alcohol compound or yields a'modified ketonic compound capable of reacting with the polyvinyl alcohol compound to form an acetal derivative thereof. Liksewise, the mono-aryl-monoalkyl ketones, such as acetophenone yield an ammonia-carbonyl condensation product which regenerates a modified ketonic product in the presence of the mineral acid catalyst and polyvinyl alcohol reactant. The modified ketone and polyvinyl alcohol compound condense in the presence of the mineral acid catalyst to form the present ketal compound, the groups R and R of the rep-.- resentative empirical formula corresponding to the alkyl or alkylene substituents attached to the carbonyl group of the modified ketone. Many of the present carbonyl compounds when reacted with ammonia yield polymeric carbonyl-ammonia addition compounds. Thus, for example, propionaldehyde forms a pentamer; butyraldehyde forms, a heptamer characterized as oxyheptaiso butylidene amine which regenerates isobutyraldehyde upon aqueous acid hydrolysis. The aldehyde and ketones may further be employed in admixture with each other or with other members of the same group toform the ammonia carbonyl reactant. Another class of compounds'utilizable in the present process, some members of which are formed by the condensation of an aldehyde or ketone with ammonia are the primary imines which yield the carbonyl compound and ammonia upon'acid hydrolysis; thus, the ammonia condensation product of benzophenone (iminobenzophenone) upon acid hydrolysis in the presence of a mineral acid catalyst yields benzophenone and the ammonium salt of the acid catalyst. Likewise fl-phenylacetaldimine hydrolyzes in acid solution to form acetophenone, condensable with the polyvinyl alcohol compound to form the present acetal products, and the ammonium salt.

The condensation of ammonia with the carbonyl compound is generally obtained readily by merely leading dry ammonia gas intothe stirred carbonyl compound until reaction ceases at a temperature of from about 0 to about 100 C. or by countercurrent contact of the ammonia gas with the aldehyde or ketone, for example, by charging the ammonia gas into the bottom of a vertical, packed tower while charging the carbonyl compound in liquid phase into the top of the tower and allowing the same to flow downwardly over the packing material in contact with the rising ammonia gas. In general, an equimolar ratio of ammonia and aldehyde or ketone is utilized in the reaction to form a rimary imine and larger than equimolar ratios of aldehyde or ketone, up to about mm 1, are preferred when preparing the aldehyde-ammonia or ketone-ammonia condensation products, particularly the polymer condensation products.

The condensation reaction of this invention, whereby a resinous product containing acetal linkages is formed, may be conducted either in the presence of certain catalytic agents or in their absence, and generally the question of whether a catalyst is to be used or not will depend upon the readiness with which the reactants tend to form the acetal linkage in its absence. The catalyst may be described as an acidic substance which may be selected from certain inorganic, strong mineral acids. When utilized, a mineral acid, such as concentrated aqueous hydrochloric or sulfuric acid containing from about 10 to acid, is preferred and is added directly to the reaction mixture in sufficient quantity and/or concentration to result in an acidic reaction mixture. Anhydrous hydrogen chloride inan anhydrous reaction system is sometimes efiective, permitting the complete utilization of the ammonia-carbonyl condensation product if a slight excess of the acid is present. The catalyst may be subsequently removed from the resinous product by contacting the mixture with a solvent which has a selective solubility for the catalyst, such as an aqueous alkaline solution, or, alternatively, the rosin may be dissolved from the catalyst in a solvent'which selectively dissolves the resin, such as benzene, methyl alcohol etc. v

When a completely esterified polyvinyl alcohol is charged into the reaction mixture, the acid catalyst serves as a hydrolyzin-g reagent as well as a condensation catalyst and under such conditions a strong and preferably concentrated mineral acid catalyst is required in order to obtain the condensation reaction L'by' the 1 simultaneous "partial "hydrolysis of the :esterand acetalation. "In such-a procedurathe. polyvinyl alcohol or its partial-esten the acid catalyst; and the ammoniacarbonyl reactant are combined prior to the reaction and heated fora period of. time sufiicient to obtain thedesireddegree of hydrolysis and acet- -'alation in the same reaction mixture. The proportion of reactants inthe reaction? mixture may-be varied to form a product containing any -desiredproportion of ester groups; free hydroxyl "groupsand acetalated hydroxy'groups, the properties'of the resultant. resin varying inxaccord- :ance withthe relative number of said groups.

Under certain conditions of reaction and when "utilizingcertain types ofreactants, it is'desirable to conduct the'reaction'in the presence of an "inert solvent'for one or more'ofpthereactants. The solvent is preferabl selected from the hydrocarbons such: as benzene, toluene, butane, "hexane, etc. and theinert halogen-substituted hydrocarbon such as ethylene dichloride, carbon tetrachloride, propylene dichloride, etc. The sol- --vent-tends to modify the rate' of reaction and the 'type of product obtained from the condensation "reaction, although'it does not of itself enter the reaction as a reactant, the products, in general being lighter incolor'than whena-reaction system is utilized inwhich the solvent is absent.

The resin-forming-reaction of the present invention may'generally be initiated at relatively low temperatures, as for example, temperatures "within. the. rangeoffrom' about 30 to about 90 -C. although'in the case;of some. reactants, the temperaturemay bezas lowasabout C. and as high as about 150 C. Superatmospheric pressures are generally unnecessary, except in the case-of the low boiling'reactants and solvents, in which caseit is desirable to utilize pressures sufficient to maintain at. least one of the vaporizable components substantially in liquid phase during the reaction. The proportion of ammoniacarbonyl reactant in the resin-forming condensation reaction mixture determines the amount of :acetal formation andth latter may be varied from slightto essentially complete acetalation. -It is generally preferred to utilize an equivalent ratio of polyvinyl-compound to ammonia-carbonylreactant of from about 1:1 to about 10:1, where the equivalent proportion of the polyvinyl .compound-is based upon the number of equiv- ;alents'of monomeric vinyl alcohol pairs in the molecule of. polymer. As indicated previously, the amount of r cross-linkage between the :reactants depends in'part-upon the number of free hydroxyl 55 --groups in jtheLstructure of the polyvinyl reactant involved in the. condensation rea'ctionywhich in *turn is determinedby'the' degree of esterification 'and/or. hydrolysis of the polyvinyl ester charged to the reaction. For the production of high melting point resins, it is desirable to have sufiicient ammonia-carbonyl reactant present in the reaction mixture to condense with a large proportion of the hydroxyl groups of the polyvinyl compound.

A typical process for the preparationof the :present resinous product comprises reacting the polyvinyl reactant, such as a completely esterified polyvinyl-acetate, with from about one-tenth to about 1 weight proportion of the condensation product of a ketone with ammonia, stirring the mixture with a slight excess of strong aqueous sulfuric acid, dissolving the resulting mixture .in vfrom about 1 to about 10 volume proportions of asuitable solvent, such as toluene and heating the; mixture .in'.a closed system to the desired "8 reaction temperature,-.generally from". about .30 to about 90 C. Following'thereaction periodzof from'about '10: minutes ,to about 2 hours,. the contents. ofthe-reactor-are cooled, diluted with 5 -water andtheprecipitated polyvinyl acetal resin washed and dried. :The resulting aqueous solution may be5.concentrated to recover the salts or subsequently treated with an alkali to liberate ammonia from'thesalt formed by reaction. of 10 thezacid catalyst with theammonia formed in the condensation reaction. The'recovered am- -monia may then be-recycled'to the initial stage of;;thereaction toform the-ammonia-carbonyl reactant for reuse therein.

."Ihe polyvinyl acetal resins formed in the pres- ..ent invention have a'wide field of utility, especially in the formulation of lacquers, adhesives, coat- ;ingcompositions, such as paints and varnishes,

laminates (for example, safety glass), molding 2O compositions, etc. One of the outstanding uses of theyresins is in the. preparation of coating compositions, such as lacquersgpaints and varnishes -where the-resin is dissolved in a suitable solvent to form a lacquer or in a-drying oil and pigment to form apaint composition. The thermoplastic type of resin' produced by thepresent process may be-molded-into various articles by hot-molding, the resin usually providinga transparent or translucentplastic-like product. The resins are-solu- -ble in various organic solvents such as the alcohols, 'inthe low molecular weight ketones such as acetone-in certain esters such as ethylacetate,

r andin various hydrocarbons such as benzene and toluene and'many of the resins are solublein drying oils of the hydrocarbon and the unsaturated fatty acid glyceride type.

.It should be pointed out that the ketals of polyvinyl-alcohol are not readily formed by the direct reaction of the ketone and the alcohol; in

the 'present'method, however, the use of ketimines,

. -ketoner-ammonia addition products, permits the preparation of such products convenientl and in good yields.

iIhe following example is introduced for the ,purpose of illustrating the process and product of the present invention. In thus illustrating a .typical procedure, it is. not intended to limit or define thescope of the invention in any of its .broad aspects in strict accordance therewith.

Example I Polyvinyl acetate having a viscosity of 15 centi- ,poises at-20" C. in benzene solution (8.6 gpper 100 .ml.; i.. e. a 1 molar solution based on the monomer) was hydrolyzed by refluxing in a dilute aqueousalcoholic solution of sodium hydroxide until the product, as shown by the acetyl number .thereof, contained only 9.5% of its original acetyl :content. The. hydrolyzed product was washed, suspended in toluene (in which it showed considerable solubility), and an equivalent amount of ,butyraldehyde-ammonia heptamer (oxyheptaisobutylidene' amine), prepared by the reaction of butyraldehyde with aqueous ammonia at 30 .C.,- was added. Sulfuric acid (50% aqueous) was slowly run into the mixture until an acid reaction .was obtained, and aslight excess then added. .The mixture was thereupon heated forthree ,hours at 50 C. following which it was neutralized and pentane added to precipitate the resin from its toluene solution. The precipitated .resin was filter dried, and the product then further dried in a vacuum desiccator. The product .was-:a polyvinyl butyralresincontaining 9.0% 75. free; hydroxyl groups. It was thermoplastic and could be readily molded at 300 F. and 1500 p. s. i. pressure.

Example II The partly acetylated polyvinyl alcohol used in Example I was, by a procedure similar to that of the previous example, reacted with the following ammonia-carbonyl compound condensation products:

fl-Phenylacetaldimine, prepared by reduction of B-phenylacetonitrile.

Hexamethylenetetramine Benzophenoneimine Hydrobenzamide, (CcHCH)3N2 Acetophenone-ammonia, (CeHsCHaC 3N2 Diacetoneamine, CHaCOCHz CNH2(CH3)2. prepared from acetone and ammonia.

In each case, a water-insoluble acetal or ketal resin of reduced hydroxyl content was produced.

I claim as my invention:

1. A process for the production of an acetal type of resinous condensation product which comprises reacting at condensation reaction conditions a plurality of reactants consisting essentially of (1) a partially hydrolyzed polyvinyl alcohol ester homopolymer and (2) a condensation product of butyraldehyde and ammonia, said reactants being reacted in the presence of a sufiicient amount of an acidic condensation catalyst to form an acidic reaction mixture.

2. The process of claim 1 further characterized in that said catalyst comprises a strong mineral acid.

3. The process of claim 1 further characterized in that said reactants are reacted in the pres- 10 ence of an inert organic solvent for at least one of said reactants.

4. The process of claim 3 further characterized in that said organic solvent is hydrocarbon.

5. The process of claim 1 further characterized in that said reactants are reacted at a temperature of from about 10 C. to about 100 C. and at sufiicient pressure to maintain the reactants substantially in liquid phase.

6. The process of claim 1 further characterized in that said reactant (1) is at least partially hydrolyzed polyvinyl acetate.

7. The process of claim 1 further characterized in that said reactant (1) is a partial ester at least hydrolyzed.

8. The resinous condensation product of a partially hydrolyzed polyvinyl alcohol ester homopolymer and a condensation product of ammonia and butyraldehyde.

HERMAN S. BLOCH.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Robitschek, Phenolic Resins, pages 31, 32, 34, 35, Iliffe and Son (London, 1950). Copy in Division 50. 

8. THE RESINOUS CONDENSATION PRODUCT OF A PARTIALLY HYDROLYZED POLYVINYL ALCOHOL ESTER HOMOPOLYMER AND A CONSENSATION PRODUCT OF AMMONIA AND BUTYRALDEHYDE. 